This invention relates to material thickness detection reflecting malfunction of a sheet transfer operation in a "Phillipsburg Inserter" type of sheet material handling machine.
In a "Phillipsburg Inserter", sheet material stored in magazines at spaced stations along a collating conveyor, are withdrawn one at a time from the bottom of stacks by the jaws of a gripper mechanism at each station and dropped onto the conveyor. A detection system is provided at each magazine station to interrupt operation when malfunction occurs because of the withdrawal of multiple sheets or no sheet during any single operational cycle. Such detection system are disclosed, for example, in U.S. Pat. No. 3,371,331 to Buckholz and U.S. Pat. Nos. 3,744,787 and 3,885,790 to Morrison.
Detection systems in the foregoing prior art installations involve synchronized sensing of the sheet material by separate contact feelers at each magazine station or by a sensing switch operator connected to the gripper jaw pivot carried by the oscillatable lever of the gripper mechanism. Such detection facilities because of space requirements are relatively inaccessible for repair and maintenance purposes and often introduce an additional source of malfunction such as jamming during the sheet transfer operation. Thus, according to the Buckholz patent aforementioned, the sheet material is contacted by a movably mounted roller to sense material thickness. Such contact roller arrangements because of wear and dust accumulations are not always reliable and are difficult to install or replace. The jaw pivot mounting arrangement for the detector according to the the Morrison patents, suffer from the same drawbacks and are furthermore difficult to visually monitor and service.
It is therefore an important object of the present invention to provide a detection system for magazine stations at which sheets are transferred to a collating conveyor by a sheet gripping mechanism, avoiding the drawbacks of prior detection systems in such installations. A further object is to provide a detection system that is easier to install, maintain and replace and which is more reliable in operation as compared to prior art detection systems in such installations.